Add support for custom exception for subclass exhaustive strategy for @SubclassMapping mapping #3821

@SubclassMapping(target = GroupSpecificationEntity.class, source = GroupSpecification.class)
@SubclassMapping(target = SiteSpecificationEntity.class, source = SiteSpecification.class)
LocationSpecificationEntity map(LocationSpecification source);

@Override
    public Target map(Source source) {
        if ( source == null ) {
            return null;
        }

        if (source instanceof GroupSpecification) {
            return groupSpecificationToGroupSpecificationEntity( (GroupSpecification) source );
        }
        else if (source instanceof SiteSpecification) {
            return siteSpecificationToSiteSpecificationEntity( (SiteSpecification) source );
        }
        else {
            throw new IllegalArgumentException("Not all subclasses are supported for this mapping. Missing for " + source.getClass());
        }
    }